Electrostatic deposition



Oct. 7, 1958 J, s n cs JR 2,855,245

ELECTROSTATIC DEPOSITION Filed Feb. 6, 1957 IN V EN TOR.

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United States Patent ELECTROSTATIC DEPOSITION John Sedlacsik, Jr.,Garfield, N. J.

Application February 6, 1957, Serial No. 638,567

9 Claims. c1. 299-1) My invention relates to improvements in anapparatus for electrostatic coating comprising a pneumatic atomizingspraying head wherein air or the like as a motive agent and a liquid orthe like as a coating agent are supplied separately to a plurality ofrelatively small discharge nozzles having'sharply defined distributingmouths and arranged in a bank upon the so-called turret of the sprayinghead. The agents are supplied to the interior of the turret and aredischarged simultaneously through the nozzles at a predetermined rate ina manner whereby the fluid agent is atomized and electrically charged.

In electrostatic coating systems of the present popular types, a fieldof electrostatic force is created which includes the article beingcoated and the atomized coating material particles in movement towardsuch article. In normal commercial practice, it is desirable to mountthe article on a grounded conveyor and thus make it an electrode atground potential. Another electrode at high potential is provided andsame usually comprises the spraying head.

This invention contemplates the formation of a paint or similar sprayfrom a liquid material, which material is capable of relatively rapidatomization and expulsion from the apparatus to which the liquidmaterial is introduced in its liquid form. This is preferably donethrough the employment of the liquid coating material atomized by amotive agent and subjected to an electrostatic attraction of theatomized particles of the material and the subsequent dispersion thereoftoward an oppositely charged article or target.

The principal object hereof is directed to a new and useful apparatusand method for improving this aforementioned dispersion of the atomizedparticles from the charging mechanism to the oppositely charged articleor target. Same is accomplished by a means which provides greaterstability to the projected spray or jet and imparts a sharper edgedefinition to the pattern thereof. That is to say, the comminutedcoating material is charged and distributed within the electrostaticfield created between the article and the issuing source of the coatingmaterial.

It is another object of the present invention to provide an improvedmethod of and apparatus for coating in which electrostatic spray formingor atomization is utilized.

Another object of the present invention is to provide apparatus forcoating by electrostatic means which is considerably simplified, moreefficient in its use, and considerably cleaner in operation.

In prior art spraying devices utilizing air pressure to atomize thecoating material, the spray mixture issuing from the spray nozzlespreads outwardly or expands uniformly taking the form of a generallyconical mist-like stream. The sides of this stream travel outwardly indiverging paths in the general direction of the surfaces to be coated.Upon impact therewith, considerable of the coating material, entrainedwith the air, is deflected in a swirling action away from this surfaceand is dispersed into the atmosphere. A great deal of the coatingmaterial, discharged from the nozzle, is thereby lost and, therefore,more material than actually needed is usually used to produce thedesired coating.

This invention has for one of its purposes, the provision of an improvedspray coating device which is capable of reducing this loss and Waste ofcoating materials, of increasing the amount of effective coverage whichmay be obtained from a given quantity of coating material, and ofgenerally improving the character of the coating produced by the spraydevice.

it will be understood that the general arrangement of the nozzles fromwhich the coating material escapes can be materially altered and theefiiciency of the apparatus can be materially increased or decreased.

More particularly, the invention contemplates a distributing apparatusand a method for applying a liquid coating to an article byelectrostatically charging and depositing the comminuted coatingmaterial upon an article to be coated which is disposed within anelectrostatic field created between the article and the issuing sourceof the coating material.

The invention includes means for imparting an electrical charge to thecoating material, which electrical charge is of such character that whenthe material is atomized, precipitated, and dispersed, the sprayingcharge is smoothly deposited upon the object toward which the atomizedmaterial is directed.

Broadly speaking, the invention relates to the formation of a paint orsimilar spray from a liquid material capable of relatively rapidatomization by expelling same from the container in which the materialis held in the liquid form.

This is preferably done by means of air, in conjunction with anelectrostatic attraction toward an adjacent target, as well as by therepulsion between the charged surface portions of the liquid and otheradjacent parts of the mass.

For such purposes, it is essential that the liquid be sprayed in such aminutely or highly atomized condition that it will difiuse readily anduniformly throughout the surrounding atmosphere.

,No completely satisfactory spraying device has yet been provided forthis purpose. It is an object hereof to provide a spray head or sprayingunit which is highly efficient and which insures uniform, widespreaddispersion of the sprayed liquid throughout a large area in anon-precipitable state of atomization.

Other objects of the invention are: to provide a multiple nozzelatomizing unit or spray head of simple and compact construction whichmay be readily manufactured at low cost; to insure equalizeddistribution of air and liquid to all of the spray outlets; to constructthe unit or spray head so that the parts thereof are readily accessible;and to provide a unit of the described character which is adaptable forpermanent installation.

Still another object hereof is to provide means for improving thedispersion and deposition of the atomized particles from a charged gunmechanism upon an oppositely charged article, which means providesgreater stability to the projected spray or jet and imparts a sharperedge definition to the. issuing pattern.

This invention broadly envisions a paint spray apparatus mechanismwherein the forward atomizing and spray elements are isolated from therearward support and control elements. The structure prevents thepossibility of a transmittal of an electrical charge from the forwardarea of the apparatus rearwardly to the rearward area thereof, the rearportion of the mechanism being at ground potential for the convenienceand safety of the operator and the forward portion of the mechanismbeing connected to the high electrical potential.

This invention is designed to be operable in combination with sprayheads such as are shown and described in the patent of John Sedlacsik,#2,710,773, issued June 14, 1955.

A source of electrostatic high potential, having one terminal groundedand its opposite terminal connected to the atomizing head creates astrong electrostatic field between the distributing head or turret andthe article to be coated, which article is also grounded.

The force of this field transforms the coating material into a spray offine, charged particles and creates an attraction which pulls the spraytoward and to the grounded article or target, thus accounting forcomplete electrostatic deposition.

The invention resides in the particular arrangement, construction andrelationship of the various elements of the spray apparatus as disclosedin the accompanying specification in which the above and other objectsof the invention will be apparent.

In the drawing:

Fig. 1 is a top plan view of the turret of the invention with certainparts broken away for purposes of clarification; and

Fig. 2 is a sectional view of the line 22 of Fig. 1.

The invention is not to be considered as limited in its application tothe details of construction and arrangement of parts illustrated inthese drawings, since the invention is capable of other embodiments. Itis to be understood that the phraseology or terminology employed hereinis for the purpose of description and not of limitation.

It will be further understood that forms of spraying devices other thanthe particular electrostatic atomizing device shown may be utilized andthat other apparatus may be employed for accomplishing the purposes andfor practicing the methods of the invention.

In the drawings, I have illustrated an example of one embodiment of theinvention wherein the parts are combined and arranged in accordance withone mode which I have devised for the practical application of theprinciples of the invention. It will be understood however that changesand alterations are contemplated and may be made within the scope of theclaims, without departing from the basic principles of the invention.

Referring now to the drawings more in detail and referring moreparticularly to the preferred form of my invention selected forillustrative purposes, I have shown an arrangement of apparatus which issuitable for coating articles (not shown) preferably moved along a pathof article movement through a coating zone into which the device of theinvention, normally fixed in location, is projected. It will beappreciated, however, that if desired, the apparatus of the inventioncould be reciprocated through this coating zone.

Disposed at one side of the path of article-movement is a horizontallypositioned atomizing head by means of which head the liquid coatingmaterial is electrostatically atomized.

I have shown an apparatus wherein an air intake line and a coatingmaterial intake line 12 are coupled by means of couplings 14 and 16respectively to a support member 18, as shown, which support member ispreferably formed from some electrical conducting material.

The support member 18 is provided with interior passageways 20 and 22whereby communication with the lines 10 and 12 respectively is afforded.

Opposite ends of a pair of plastic tubes 30 and 32, one concentricallydisposed within the other (as will be best observed by reference to Fig.1), are received within spuds 34 at opposite sides of the support member18 and are held relative thereto by means of couplings 36 in theconventional manner. Said tubes function as insulations as willhereinafter be observed.

A packing member 38 is seated within each coupling 36 adjacent therespective spud 34 so as to insure a tight 4 fit between the couplingand the respective adjacent end of the tubes.

The inner tube member 32 has a central orifice or passagewaytherethrough which is in communication with the passageways 20 and 22 ofthe member 18.

Disposed within the member 32 throughout the length thereof is aflexible rod-like member 40 formed of electrical conducting material,which member is protected by the tubes 30 and 32 disposed therearound.

Opposite free ends 42 of the member 40 are secured to the member 18within the passageways 20 and 22 so as to establish electrical contacttherewith for purposes as will shortly appear.

The member 18 is connected by means of a connection 5t) fixed thereto bya screw 52 or equivalent means to one terminal or pole of a staticmachine or other source of high electric potential.

The members 30 and 32 are looped in a ring-like manner as shown and atthe forward side thereof a plurality of forwardly disposed transverselyextending nozzles 60 are provided.

Each nozzle 60 is made of a plastic similar to the material of member 30and is seated over an opening in the side wall thereof as shown so thateach nozzle communicates with the interior of the member 32.

Each nozzle 60 is provided with a hollow interior 62 having an outermostrestricted throat 64 leading outwardly to and through the outer free endor mouth 66.

Extending upwardly into the opening 62 of each nozzle and terminating inan outer free end just short of the restricted throat 64 thereof is aneedle-like member 41 which is fixed at its inner end to the member 40and extends through a suitably aligned opening through the wall of themember 32, the opening being of suitable dimension so as to permit theescape of the motive agent and the fluid agent therethrough around theneedle member 41.

The air or equivalent motive agent is introduced to the apparatusthrough the air intake line 10 and through the air passageway 20 of themember 18 and thence outwardly into the hollow passageway of the member32.

The fluid coating material is similarly introduced to the apparatusthrough the coating material intake line 12 and through the coatingmaterial passageway 22 of the member 18 and thence outwardly into thehollow passageway 0f the member 32.

The motive agent and the fluid agent travel in opposite directions fromthe member 18 through the member 32 where they are mixed within thecentral orifice of the member 32 as they are brought together from theopposite ends thereof. Being under pressure from said opposite ends, themixed materials are urged outwardly through the members 60 for dischargein a forward direction through the months 66 thereof.

As the stream of mixed air and liquid passes outwardly through theopenings in the member 32 around the surfaces of the needles, the sameare subjected to the atomizing effect of the corona discharge from theelectrode whereby the finely divided particles comprising the sprays areeach imparted electrical charges of like polarity.

With voltage applied directly to the rod member 40 of the spray headstructure, a corona discharge is formed in the region around the member40 and around the needles and adjacent the outermost peripheries of theneedles. This discharge is of an intensity sufficient to complete thebreak up into particled form the coating material being discharged fromthe nozzles and to project said coating material in a spray form towardthe surface of the article being coated.

That is to say, in actual operation, the electrical energy is maintainedat the high potential nozzle spray assembly. The material being atomizedand the gas are delivered through the respective openings to the nozzleor head assembly.

The material being atomized and the gas are delivered through therespective delivery tubes and connections to the head assembly. Thematerial and gas are released in the form of high velocity streams wherethey meet and mix with each other under pressure, are atomized andelectrically charged, and pass outwardly with high turbulence.

As previously stated, under certain conditions, the projected jet waverserratically and continuously. This results in a scattered dispersion ofthe particles comprising the jet and thereby causes the depositedpattern upon the article to have irregularly disposed lakes. Inaddition, the mutual electrical repulsion of the particles due to theirbeing charged to the same sign causes them to spread and scatterlaterally, particularly at the outer portions of the jet. This makes aless sharply defined edge at the boundary of the deposited pattern.

To overcome these objectionable characteristics, I provide a gaseousfield surrounding in close proximity the electrostatic atomizing fieldand coextensive in length with the latter, within each of the nozzles.

The liquid and gaseous materials are supplied through their respectiveconduits to the nozzle assemblies as previously described.

The mixed materials issue from the orifices at the outermost free endsof the nozzles in the form of streams. The mixtures are directedoutwardly with high turbulence in the form of finely atomized streams.

In operation, a unidirectional electric potential is maintained at thehigh potential nozzle assembly and, as the thus formed stream isdirected outwardly away from the nozzle, it is subjected to the ionizingefiect of the corona discharge from the isolated nozzle whereby thefinely divided particles comprising the spray are each impartedelectrical charges of like polarity and of substantially equalpotential.

The positively charged particles tend to repel one another and thusresist coalescence with the result that the electrified cloud of sprayis attracted to the grounded object to be sprayed and/or coated. Theparticles are attracted to and precipitate in a layer upon the nearestsurface of the grounded article which is to be coated.

As aforesaid, the spray head is connected to a source of high voltage(not shown) through one terminal thereof. The other terminal of thesource is grounded and through ground is connected with the articles tobe coated and/or the conveyor therefor,

Accordingly, the space of field between the spray head and article iselectrostatically charged by reason of the article being grounded andthe spray head being at the high potential.

The effect thereof is to cause an electrical force to act on the coatingmaterial causing same to be broken up into finely divided or minuteparticles of coating material, such as to be attracted to the groundedarticle for deposition thereon. Thus, the grounded article may bereferred to as a collecting electrode of one potential with theapplicator head serving as a discharge electrode of a differentpotential.

The electrostatic force set up on the field between the electrodes issuch as to develop and transmit finely divided particles of the coatingmaterial from one electrode to the other.

The same action will take place when the spray head is grounded and thearticle is directly connected with the source of high voltage and ischarged at a high potential.

The rate at which the coating material is supplied to the spray head maybe controlled by valves or the like (not shown) so as to insure that theapparatus will not receive more coating material than can be atomizedfrom its discharge edge.

With voltage applied directly to the spray head structure, a coronadischarge is formed in the region around and adjacent each needle whichis of an intensity sufi'i- 6 cient to break up or to atomize intoparticled form the coating material and to project said coating materialin a spray form toward the surface of the article being coated.

By means hereof, the coating material is charged before the emissionthereof from the nozzles 60 by means of the elongated charging surfaceof the needle like members 41 within the nozzles 60 and by means of thered like member extending through the passage of the member 32.

The coating material, by means hereof, absorbs a more complete chargewithin the spray device than has been heretofore possible with prior artsystems where the electrical charges have been imparted to the particlessubsequent to discharge from the mouth of the device in the areaimmediately forward thereof.

That is to say, in actual operation, the electrical energy is maintainedat the high potential atomizing head assembly. The material beingatomized is delivered through the delivery tube and connections to thehead assembly.

Without further analysis, the foregoing will fully reveal the gist: ofmy invention whereby others can, by applying current knowledge, readilyadapt it for various applications without omitting features which, fromthe standpoint of prior art, fairly constitute essential characteristicsof the generic or specific aspects of this inven tion. Such adaptationstherefore should and are intended to be comprehended within the meaningand range of equivalence of the claims below.

I claim:

1. Apparatus for electrostatic coating comprising, a support, an airintake line coupled to said support, or coating material intake linecoupled to said support, an air passageway in said support communicatingwith said air intake line, a coating material passageway in said supportcommunicating with said coating material intake line, a primary plastictube communicating with said air passageway at one end thereof and withsaid coating material passageway at the opposite end thereof, a flexibleelectrical conducting member fixed to said support member at oppositeends thereof and extending through said tube, a plurality of nozzlesconnected to said tube and communicating with the interior of said tube,all adapted and arranged whereby air and coating material are mixedwithin said tube before passing outwardly through the nozzles of saidplurality thereof.

2. In the apparatus of claim 1, each of the nozzles of said pluralitythereof being provided with a needle-like member extending upwardlytherethrough from said conducting member.

3. In a pneumatic spraying head comprising a high potential electrode towhich a motive agent and a liquid coating agent are separately suppliedcomprising, a support connected to motive agent and liquid coatingmaterial intake lines and having separate motive agent and liquidcoating material passages communicating therewith and extendingtherethrough, a turret of non-conducting material having a passagewaytherethrough having one extremity communicating with the motive agentpassage of said support and having its opposite extremity communicatingwith the liquid coating material passage of said support, an elongatedinsert of electrical conductivity extending through the passageway ofsaid turret and connected to the high potential source, a plurality ofrestricted discharge ports extending outwardly from said turret andcommunicating with the passageway thereof, and a plurality of dischargeelectrodes each being disposed within each of said discharge ports, eachof said discharge electrodes being fixed to said insert.

4. Apparatus for use in an electrostatic coating system, said apparatuscomprising a support having two separate passages therein, one passagebeing for air and the other passage being for a coating material, saidsupport including intakes for each of said passages and having outletsdisposed in line with each other but pointing in opposite directions, apair of concentric flexible tubes of electrically insulating material,one end of said 'co'n'centrictub'es being coupled to one outlet and theother end of said concentric tubes being coupled to the other outlet, aflexible electrical conductor disposed within the inner insulating tubeand electrically connected to said support, a plurality of nozzles ofinsulating material carried by the outer tube and extending outwardlytherefrom, said nozzles communicating with the interior of the outertube by means of openings in the wall of the outer tube at the bases ofsaid nozzles, said inner tube having openings through the Wall thereofaligned with the outer wall openings for said nozzles, and a metallicmember for each nozzle electrically connected to said conductor withinthe inner tube extending through the openings in the concentric tubesand into the nozzle, said flexible tubes being adapted to carry air andcoating material in counterfiow relation and said nozzles dischargingsaid coating material in atomized form and said conducting member beingadapted to charge said stream of atomized material as it issues fromeach nozzle.

5. An electrostatic coating means comprising a tubular loop likemanifold, at least a part of the interior surface portion of saidmanifold being of insulating material having 'a source of air connectedto one leg thereof and a source of coating material attached to theother leg thereof, an electrical conducting member in said manifoldhaving attached thereto a source of electrical potential, and at leastone nozzle extending from said tubular manifold.

6. An electrostatic coating means comprising a tubular loop likemanifold as set forth in claim 5, and wherein said nozzle has disposedtherein a branch conductor portion connected to the electricalconducting member.

7. An electrical coating means comprising a tubular loop like manifoldas set forth in claim 5, and wherein a multiplicity of nozzles extendfrom said tubular manifold and are spaced from one another, and witheach of said nozzles having a conductor therein and with one end of eachsaid conductor being connected to said electrical conducting member.

8. An electrical coating means comprising a tubular loop like means asset forth in claim 5, and wherein a plurality of nozzles extend fromsaid tubular manifold with each of said nozzles having an outer portionof insulating material and an internal conductor portion connected atone end to said electrical conducting member and the other end thereofterminating within the References Cited in the tile of this patentUNITED STATES PATENTS 2,302,185 Campbell Nov. 17, 1942 2,302,289Bramston-Cook Nov. 17, 1942 2,710,773 Sedlacsik June 14, 1955 2,766,064Schweitzer Oct. 9, 1956 2,782,074 Sedlacsik Feb. 19, 1957 FOREIGNPATENTS 688,433 Great Britain Mar. 4, 1953

